Polyvinyl acetal resins



Patented June 13 1939 Um'rao s'rA'ras PATENT OFFICE assms; 1

No 1mm. amass. October 22, ms.

sen-rm.

merised vinyl esters as polyvinyl acetate) is a water-soluble substance which can be reacted with aldehydes to form resinous materials. Most of these materials previously disclosed in the art are thermoplastic, and difler from polyvinyl alcohol itself in that'they are not soluble in water, but are soluble in a wide variety of organic substances, including many water-insoluble solvents, such as aromatic hydrocarbons, chlorinated hydrocarbons and various esters. As in the case of the simple alcohols, polyvinyl alcohol combines with aldehydes in the proportion of two molecular equivalents of its theoretical monomer, vinyl alcohol, to each molecular equivalent of aldehyde. Because these reaction products are analogous to the alkylidene diethers, they are usually called polyvinyl acetal resins. Two rea lated members of the poylvinyl acetal class also are known. One includes the substances formed by the reaction of aldehydes with partially hydrolyzed polyvinyl esters, and these resins contain principally ester and acetal groups in their molecule. Such substances may be termed polyvinyl acetal-ester resins, and they are intermediate, in general properties and solubility characteristics, between the polyvinyl acetals and the polyvinyl esters. The other type of product may be termed polyvinyl alcohol-acetals, and are formed by the reaction of adlehydes with polyvinyl alcohol to an extent insuilieient to render the product soluble in water-insoluble esters and the like, and thus are closely related to polyvinyl alcohol itself.

Polyvinyl esters, polyvinyl alcohol, the polyvinyl acetal resins. polyvinyl acetal-ester resins, and

the polyvinyl alcohol-acetals referred to, may

each form the basis of film-forming or plastic compositions. In general, these resins may be softened, or. plasticized, to increase their flexi-,

btlity by means of the solvents in which they are soluble. 'I'huapolyvlnyl esters. polyvinyl acetals and polyvinyl ester-acetal resins may be softened by the addition of high-boiling esters (which are solvents for these materials) and polyvinyl alcohol and thepolyvinyl alcohol-actetals may be (01. zoo-1s) softened by was of water (the only am solvent for polyvinyl alcohol). In the latter case,

,the volatility of water and its consequenttendency to be lost from .the compositions can be partially oirset by the use of hygroscopic agents, 5 such as glycerine, in the compositions. This expedient has been proposed as particularly fruitful in the case of the polyvinyl alcoholacet which, even when not soluble in water. are hi my water-absorptive and are rendered 10 soft and flexible by water, with or without added glyce'rinef The polyvinyl alcohol-acetals which are not soluble in water are usually soluble in the lower aliphatic alcohols and may be plasticized and rendered extensible by means of such scll6 vents. The flexibility of these compositions almost invariably increases with and in direct proportion to the quantity of solvent plasticizer added. when the piasticized compositions are subjected to tensile tests and the elongation observed as a function of the load applied, it will' be seen that, as the amount of solvent plasticizer in the composition is increased. the load required to produce a given elongation is markedly decreased. 25

Because of this fact, the resins discussed, when suilicientiy plasticized to have high flexibility and extensibility, yield compositions of greatly reduced ultimate strength as compared with the unplasticized material. In addition, such compositions lack elasticity; that is, while they are flexible. they do not recover their original dimensions after the load applied is removed. The properties of compositions of these resins cannot be improved by attempting to soften the water- 5 soluble polyvinyl alcohol or the polyvinyl alcoholacetals with non-solvent plasticizers, such as the high-boiling esters. or' by attempting to plasticize the ester-soluble. polyvinyl esters, polyvinyl acetals. or the polyvinyl ester-acetals with water, 40 owing .to the complete lack of compatibility of the ingredients of such systems. 'Ihuawhere flexible andhighly extensible compositions of. the resins discussed are required. it is necessary to soften the resins with plasticizers that are also" 5 solvents for the resins, with the inevitable result that products of low ultimate strength are sccured which are almost entirely without e1asticity. In addition, the polyvinyl esters. polyvinyl acetals and polyvinyl acetal-esters, when softened so with solvent plasticizers, are softened by heat at temperatures much below the heat softening temperatures of the unplasticised material, while polyvinyl alcohol and polyvinyl alcohol-acetals,

when softened by water or water-soluble this. so

have been found to be lacking in adhesive properties for glass. metal, or other smooth surfaces.

The primary object of this invention is to provide a class of inherently colorless artificial resinous materials which are largely free from the defects lust discussed, and which can be softened ofilth water-insoluble ester plasticizers to yield h ogeneous compositions oi excellent clarity and adhesiveness which have lasting properties of flexibility, resilience and elasticity, coupled with great strength and toughness. The invention also includes plasticized compositions of the new resins. and the methods of making these resins .to smooth surf The new resins which enable the obiects of the invention to be achieved may be classed as polyvinyl aleohol-acetal resins, or polyvinyl partial acetal resins, or a very definite composition, and the composition of these particular resins was not at all predictable from a study of known resins of related types. The new resins are made by the reaction of certain aldehydes with polyvinyl alcohol or polyvinyl esters, and, in general, to obtain materials of adequate strength, the polymeric vinyl compound from which they are formed should have an average macromolecular weight of at least 7,000. Resins made according to this invention from polyvinyl bodies having average molecular weights in excess of 25,000 yield plasticiaed compositions of exceptionally high tensile strength and are the preferred resins of my invention. (Molecular weights referred to herein are calculated by means of Staudinger's formula from viscosity determinations on. solutions of the materials.)

The resins contemplated by this invention are limited both by the nature and the quantity of the aldehyde contained in them, and these resins contain substantially only free hydroxyl groups of polyvinyl alcohol and acetal groups in their molecule. The proportion of aldehyde or acetal in the new resins will be indicated throughout as percent acetalization (which indicates the percentage of hydroiwl or functional groups in the polymeric body that are combined with aldehyde), and'it is to be understood that my new resins are free from ester groups or any other groups in amounts suflicient to aii'ect the solubility or other characteristics of the materials.

The aldehydes from which my new resins are made are butyraldehyde, propionaldehyde and valeraldehyde, and the order of preference among these three aldehydes is that given. The extent of acetalization for my new resins is diiferent for each aldehyde. In any case, the degree of acetalization with the aldehyde material containing at least one of the saturated aliphatic aldehydes having from 8 to carbon atoms in its molecule must be so correlated with the kind of aldehyde and the free hydronyl groups in the resin that the product has those properties characterizing the resins of this invention. Thus, with butyraldehyde, the resins must be acetaliaed between about 54% and about 70%: with propionaldehyd between about 52% and about 88%: and. with valeraldehyde, between about 39% and about 58%. These diiferenees are occasioned by the fact that the properties of the resins have been found to vary with the length of the hydrocarbon chain 0! the-aldehyde used, and the degrees oi acetalization recited above have been found by test to be those which delimit resins of substantially the same properties.

This application is directed specifically to those resins made from butyraldehyde, and resins made from propionaldehyde and valeraldehyde are the subjects 0! my copending applications Serial Nos. 265.515 and 265,516, died April 1, i939.

I have tried to make resins equivalent to those Just defined using other aldehydes, but, so far as I have-been able to determine, resins which are fully the equivalent of those of this invention with respect to colonstrength br solubility characteristics cannot be formed from aldehydes of less than three or more than flve carbon atoms regardless of their degrees of acetalization. Thus, certain of the desired qualities of the new resins may be obtained in resins made from acetaldehyde within certain narrow limits of acetalization, and certain other of the desired characteristics may be provided in resins acetalized with hexaldehyde within certain other narrow limits, but in no case have I found it possible to make resins from either of these two aldehydes which have all, or nearly all, of the outstanding prop erties of the resins specified above. Using formaldehyde alone or aldehydes higher than hexaldehyde, it is, so far as I have ascertained, not possible to make resins which have the qualities oi the resins of this invention to any significant extent.

The resins of this invention are not soluble in water, but, unlike the polyvinyl ester, polyvinyl acetal and polyvinyl acetal-ester resins previously known. they are also, in general, not soluble in water-insoluble organic solvents at ordinary temperatures. (The term "ordinary temperatures" as used herein refers to temperatures below 40 (3.; usually 30 0., or lower). they are not dissolved at ordinary temperatures by ester plasticizers, although the new resins themselves have the unusual property of absorbing or dissolving sufllcient quantities of ester plasticizers to yield adequately softened, homogeneous compositions. For example, the new resins at ordinary temperatures are generally insoluble in such organic liquids as aliphatic and aromatic hydrocarbons; in ketones; in chlori-' nated hydrocarbons, including ethylene dischloride, methylene chloride and chloroform; or in esters. such as ethyl acetate, diethyi phthalate and polyethylene glycol hexoates. Portions of the more highyl acetalized resins of this invention may dissolve in certain of the chlorinated hydrocarbons or in certain of the ketones, but this partial solubility in the ketones and chlorinated hydrocarbons in no way indicates that such resins are beyond the scope of this invention or are lacking in the new properties which characterize the resins oi this invention. These resins are, in general, soluble in water-soluble liquids, such as the alcohols, glycol monoalbl ethers and the like, except certainof the polyvinyl valeraldehyde acetal resins, which are insoluble in the lower alcohols. In any case, the most outstanding characteristic oi the new resins is their virtual insolubility in water-insoluble ester plasti- Similarly,

157 known. Their heat softening temperatures,

in general, are inversely proportional both to the degree of acetalisation and to the number of carbon atoms in the aldehyde used in the formation of the resins.

Plastic compositions having high flexibility coupled with high ultimate strength are of extreme importance for such specialised uses as the inner layers for laminated saiety glass, where it is desirable to use a material having high flexibility in order to absorb the force of a blow over considerable displacement. It is also very desirable that the plastic have a high ultimate strength coupled with flexibility in order that an object striking the laminated glass will be restrained from continuing through it after its velocity has been reduced by the yielding inner layer. These desirable properties cannot be obtained in plastic compositions made from the known polyvinyl ester, polyvinyl acetal, polyvinyl acetal-ester, polyvinyl alchol, or polyvinyl alcohol-acetal resins when rendered flexible by means of solvent plasticizers because, aspointed out above, the ultimate'str'ength of such compositions is reduced greatly when these materials are made flexible by such plasticizers. In general, plastic compositions having high flexibility and elasticity and high ultimate strength may be defined as those which have an elongation, when subjected to tensile tests at ordinary temperatures, of at least about 200% and which do not fail at loads of less than about 2,000 pounds per square inch. The resins of this invention when adequately plasticized yield homogeneous compositions which usually surpass the limits set forth.

For example. a composition was made which consisted of 69% by weight of a polyvinyl partial acetal resin 66% acetaliaed with butyraldehyde. colloided' with 31 by weight of triethylene glycol di(2-ethyl butyrate). At atmospheric temperatures this resin is insoluble in the plasticizer' named, but, by various expedients known in the art. the resin and plasticizer can be combined to form clear and homogeneous compositions. The stress-strain characteristics of this composition were determined by subjecting specimens of it to increasing loads on a tensile testing machine while observing the elongation as a function of the load applied. The samples of this composition tested at. atmospheric temperature were found to have an elongation of about 250% with an ultimate tensile strength of about 3,300 pounds per square inch.

The stress-strain properties of another composition also containing 31% by weight of triethylene glycol dii2-ethyl butyrate) and 69% by weight of a polyvinyl acetal resin were determined in a parallel test under identical conditions, but the resin in this case was more than acetallzed with butyraldehyde and was almost completely soluble in the plasticizer at ordinary temperatures. This composition possessed tensile properties vastly difierent from that first discussed, and, although its elongation was around 300%, its ultimate tensile strength was less than 100 pounds per square inch.

Inathirdtestunderthesameoonditionathe stress-strain properties of a plastic composition formed from a polyvinyl acetal resin which was about 44% acetalised with butylraldehyde were observed. In this composition the plasticiaer again was trlethylene glycol dim-ethyl butyrate) and the resin was insoluble in the plasticizer at ordinary temperatures. However, this resin also was not compatible with amounts oi the plasticizer sumcient to render it elastic or extensible. and homogeneous compositions containing more than 10% by weight of the plastlciaer could not be formed. A compdsition containing by weight of the resin and 5% by weight of triethylene glycol dim-ethyl butyrate) was found to be homogeneous and was used in this test. The tensile properties of this composition ditrered greatly from either of those Just and, although the ultimate tensile strength of the composition was 4,500 pounds perwquare inch, its elongation to its breaking load was less than 25%. V

It is the elastic and tensile properties of the plasticized compositions made from the polyvinyl partial aeetal resins of my invention which render the new resins so useful in the manuracture ofpon-shattering laminated glass. for coating fabric materials, and in many other uses, and which also distinguish these new resins from all of the known polyvinyl acetals and related classes of. vinyl resins.

The resins of this invention may be formed from polyvinyl alcohol by reaction with aldehyde material containing at least one saturated aliphatic aldehyde having from 3 to'5 carbon atoms in its molecule in the presence of an acidic substance as a catalyst. Polyvinyl alcohol itself may be used as the starting substance, or the reaction with aldehyde may proceed simultaneously with the hydrolysis, alcoholysis or saponification of a polyvinyl ester. For example, resins of uniform quality result when a water solution of the polyvinyl alcohol is acidified with an inorganic acid substance, preferably a mineral acid, such as hydrochloric or sulfuric acid, and the aldehyde added with constant stirring. Before any or the acetal resin is allowed to precipitate from the aqueous reaction mixture, anorganic solvent for the resin which is miscible with water is added to maintain the resin in solution. Examples oi such solvents are methanol, ethanol and isopropanol. By adding suitable amounts of the organic solvent (acidified if necessary) as the aldehyde is added. any desired proportion of aldehyde and polyvinyl alcohol within the ranges set forth may be reacted while the entire system is maintained as a single liquid phase.

An example of the conduct of the process according to the method just described is given below for purposes of illustration:

53 parts by weight of polyvinyl alcohol was dissolved in 547 parts by weight of water, to which 35.4 parts by weight of aqueous H01 (87% hydrogen chloride) was added. This solution was stirred, and 8.1 parts by weight of butyraldehyde was added. Before any resin could be precipitated from this solution, a portion ofacldifled isopropyl alcohol was added to maintain the resin in solution. Additional butyraldehyde and acidified isopropyl alcohol were added intermittently until a total of 32.2 parts by'weight of butyraldehyde, 800 parts by weight of isopropyl alcohol and 02.6 parts by weight of aqueous H01 (37% hydrogen chloride) had been added.

After standing for about an hour, this solution became hazy and a soft resin, which was almost soluble in the alcohol-water mixture. began to separate. This resin was precipitated by adding water to the reaction mixture, and the separated resin was re-dissolved in methanol. Residual acid in this solution was neutralized by adding potassium carbonate, and the salt precipitate was filtered out. The contained resin was again precipitated with water, after which it was thoroughly washed and dried.

The degrees of acetalization of the specific resins referred to above wa'e calculated from the quantities of aldehyde in the resins as determined by the following method:

A 2-gram sample of the dry resin is accurately weighed and placed in a 500 cc. Erlenmeyer flask with 50 cc. of normal butanol and 50 cc. of half normal hydroxylamine hydrochloride solution. The sample is then refluxed for two hours in parallel with a blank. Thereafter, 50 cc. of methanol together with brom phenol blue indicator is added and the mixture titrated with half normal sodium hydroxide solution. From the difference between the titrations of the sample and the blank there may be calculated the amount of hydrochloric acid liberated from the hydroxylamine hydrochloride on the combination of hydroxvlamine with aldehyde. From this value the quantity of aldehyde present in the resin, or its degree of acetalization, may be calculated.

Modifications of the invention will be apparent to those skilled in the art. For example, if large variations are made in the amounts of plasticizer to be incorporated with the resin or in the allowable water absorption or heat softening point of the resin, the composition of the resin may vary from those specifically set forth above. In addition, the resins may contain a limited proportion of ester, ketone, other aldehyde or functional groups normally foreign to the resins of this invention, but in any case it is essential that such variations as are made in the resin composition, or the presence of such functional groups other than free hydroxyl and acetal groups of the aidehydes set forth within the limits recited, must not be sufllcient to affect the solubility properties which are characteristic of the new resins, primarily, that ability of the resin to form, with water-insoluble ester plasticizers, homogeneous compositions which are elastic and highly extensible while retaining high ultimate strength. The polyvinyl partial acetal resins which are modified in non-material respects as indicated are included within the scope 01 this invention, which should not be limited other than as defined by the appended claims.

This application is, in part, in continuation of my copending application Serial No. 741,997, filed August 29, 1934, and in continuation of my copending application Serial No. 115,476, flied December 12, 1936.

I claim:

1. A tough and strong artificial resin substantially identical with a resin resulting from the condensation of polyvinyl alcohol with suflicient butyraldehyde to combine with from about 54% to about 78% of the hydroxyl groups of said polyvinyl alcohol, the total extent of acetalization and the proportion, of free hydroxyl groups in said resin being so correlated that said resin is substantially insoluble in triethylene glycol di(2- ethyl butyrate) plastioizer at ordinary temperatures but'is compatible with substantial quantities of said plasticiaerto form therewith flexible and elastic compositions which have at ordinary temperatures an elongation oi at least about 200% and an ultimate strength above about 2,000 pounds he! Bqllare inch.

2. A tough and strong artificial resin substantially identical with a resin resulting from the condensation of polyvinyl alcohol with aldehyde material comprising butyraldehyde. the total extent of aldehyde combination in said resin and the proportion of free hydroxyl groups thereof being so correlated that said resin is substantially insoluble in triethylene glycol di(il-ethyl butyrate) plasticizer at ordinary temperatures but is compatible with substantial quantities 01 said plasticizer to form therewith flexible and elastic compositions which have at ordinary temperatures an elongation of at least about 200% and an ultimate strength above about 2,000 pounds per square inch.

3. A tough and strong artificial resin composed of a polyvinyl partial acetal resin acetalized with butyraldehyde between about 54% and about 7 the degree of acetalization with butyraldehyde and the proportion oi tree hydroxyl groups in said resin being so correlated that said resin is compatible with substantial quantities of triethylene glycol di(2-ethyl butyrate) plasticiaer while being virtually insoluble in said plasticizer at ordinary temperatures.

4. A strong and resilient homogeneous composition of matter having an elongation of at least about 200% and an ultimate strength above about 2,000 pounds per square inch at ordinary temperatures, which is' essentially composed of a water-insoluble ester plasticizer and a polyvinyl partial acetal resin substantially identical with a resin resulting from the condensation of polyvinyl alcohol with suflicient butyraldehyde to combine with from about 54% to about 78% of the hydroxyl groups of said polyvinyl alcohol, the total extent of acetalization and the proportion of free hydroxyl groups in said resin being so correlated that said resin is substantially insoluble in said plasticizer at ordinary temperatures but is compatible with a substantial quantity of said plasticizer to yield said homogeneous composition therewith.

5. A tough and strong composition of matter essentially composed of a water-insoluble ester plasticizer and a polyvinyl partial acetal resin acetalized with butyraldehyde between about 50% and about 78%, the degree of acetalization with butyraldehyde and the proportion of free hydroxyl groups in said resin being so correlated that said resin is virtually insoluble in said plasticizer at ordinary temperatures but is compatible with substantial quantities of said plasticizer to yield flexible and resilient homogeneous compositions therewith.

6. Process for making polyvinyl partial acetal resins which comprises forming a water solution of polyvinyl alcohol; adding to said solution an inorganic acidic substance, an aldehyde, and an organic solvent which in admixture with water is capable of dissolving said resins; the total quantity of aldehyde added being insuflicient to react with all the polyvinyl alcohol present; and the rates at which said acidic substance, said aldehyde, and said organic solvent are added being such as to maintain the whole in liquid phase.

'7. Process for making polyvinyl partial acetal resins which comprises forming a water solution of polyvinyl alcohol; adding to said solution an resins which comprises forming a water solution of polyvinyl alcohol; adding to said solution an inorganic acid, butyraldehyde. and an alcohol which in admixture with water is capable of dissolving said resins; the amount oi. butyraldehyde added being sumcient to react with from about 54% to about 78% 01' the hydroxyl groups of the polyvinyl alcohol present: and the rates at which said acid, said butyraidehyde, and said alcohol are added being such as to maintain the whole in w liquid phase.

HAROLD 1". ROBERTSON.

CERTIFICATE or comcrron.

Patent n 2,162,673.

HAROLD F. ROBERTSON.

June 13, 1939. A

It ie hereby certified that error appears in the printed specification or the above numbered patent requiring correction as follows: Page 2, sec-- ond column, line 57-53, for "diechloride" read dichioride; line 61, for 'highyl" read highly; page 1;, second column, line 51;, claim 5, for "509 read 51 and that the said Letters Patent should be read with this cor-- reetion therein that the same may eonformto the record or the case in the Patent Office Signed and sealed this 22nd day of August, A. D. '1959.

(Seal) Leslie Frazer Acting Commissioner of Patents.

resins which comprises forming a water solution of polyvinyl alcohol; adding to said solution an inorganic acid, butyraldehyde. and an alcohol which in admixture with water is capable of dissolving said resins; the amount oi. butyraldehyde added being sumcient to react with from about 54% to about 78% 01' the hydroxyl groups of the polyvinyl alcohol present: and the rates at which said acid, said butyraidehyde, and said alcohol are added being such as to maintain the whole in w liquid phase.

HAROLD 1". ROBERTSON.

CERTIFICATE or comcrron.

Patent n 2,162,673.

HAROLD F. ROBERTSON.

June 13, 1939. A

It ie hereby certified that error appears in the printed specification or the above numbered patent requiring correction as follows: Page 2, sec-- ond column, line 57-53, for "diechloride" read dichioride; line 61, for 'highyl" read highly; page 1;, second column, line 51;, claim 5, for "509 read 51 and that the said Letters Patent should be read with this cor-- reetion therein that the same may eonformto the record or the case in the Patent Office Signed and sealed this 22nd day of August, A. D. '1959.

(Seal) Leslie Frazer Acting Commissioner of Patents. 

